1. Field of the Invention
The present invention relates to a field emission type cold cathode element, a method of fabricating the same, and a display device. In particular, the present invention relates to: a field emission type cold cathode element which is formed on a glass substrate and provide a low element resistance in operation and a high element resistance upon electric discharges; a method of fabricating the same; and a display device.
2. Description of the Related Art
Conventionally, field emission type cold cathode elements of Spindt type are known in which acute emitters of cone shape and a gate electrode formed close to the emitters, the gate electrode having submicron openings therein, are used to concentrate high electric fields at the extremities of the emitters so that electrons are emitted in vacuum from the extremities of the emitters to a typically-opposed anode electrode to capture the emission current.
Other elements are also known in which a gate electrode is arranged close to emitters formed of silicon cone elements or materials having smaller work functions, and a field is applied thereto to cause electron emission.
Surface conduction type elements are also known in which an electric current is passed through two electrodes having a minute gap therebetween so that electrons discharged across the gap between the electrodes strike the opposite electrode to cause emission of secondary electrons which are taken into an anode electrode provided in vacuum.
Moreover, in display devices using cold cathode elements, such as a filed emission display (FED), phosphors corresponding to three primary colors, i.e., red, green, and blue are provided in vacuum so as to oppose the emitter, and added with a transparent electrode or thin film metal to form an anode, on which a voltage is impressed to inject emission electrons into the phosphors for light emission. This can provide self-luminous display devices, featuring independence of color properties from view angle.
Among these field emission type cold cathode elements, however, the Spindt type elements in which high electric fields are concentrated at the extremities of the emitters so that electrons are emitted from the extremities of the emitters in vacuum and the elements in which a gate electrode is arranged close to emitters formed of silicon cone elements or materials having smaller work functions and a field is applied thereto to cause electron emission have a problem in that a discharge occurs between the gate and an emitter or between the gate and the anode to end up with a high current, causing breakdown of the element.
An approach to avoid this is to provide high-resistance layers formed of poly-crystalline silicon or amorphous silicon in series with the emitters to prevent the breakdown-causing high current from flowing through the element.
Another approach is to adopt trenching technologies to make trenches, into which insulating films are embedded to form oblong crystal regions surrounded by the insulating films on all sides. This offers nonlinear resistive elements, preventing a high current from flowing (Japanese Patent Application Laid-Open Nos. Hei 10-50201 and Hei 10-12128).
In the case where poly-crystalline silicon or amorphous silicon is used to provide emitters with resistive layers, the resistive layers can be increased in resistance to reduce the current flow upon discharges, thereby improving resistance against the discharge breakdown of the element. The resistive layers, however, are connected in series with the emitters, so that they act as resistances even in normal operation, producing a voltage drop across the resistors. This accordingly increases the operating voltage for driving the element. A problem arises particularly with higher emission currents in that the voltage drop becomes greater to increase the operating voltage.
In contrast, conventional emitters that comprise nonlinear resistive elements adopting the trenching technologies will act as high resistances when a discharge current flows therethrough, whereas they serve as low resistance in normal operation with a smaller effect of voltage drop. In this case, however, the trench structures are formed, e.g., in a silicon single crystal with a trenching depth of 5 xcexcm or more.
Field emission type cold cathode elements are adapted to a display device by using a glass substrate. Here, it is impossible to grow a single crystal on this glass substrate, and even if poly-crystalline silicon is used instead, a problem arises in that poly-crystalline silicon layers are extremely hard to generate in a thickness of 5 xcexcm or more.
Besides, the poly-crystalline silicon layers have crystal interfaces, which makes it extreme hard to form satisfactory trench structures. The interfaces also introduce large irregularity among elements, producing a problem in that such elements are not suited to uniformity-requiring devices such as a display.
An object of the present invention is to provide a field emission type cold cathode element having the nonlinear characteristics of providing a low resistance in normal operation and a high resistance upon discharges even with the use of a glass substrate or the like.
Another object of the present invention is to provide a method of fabricating the same and a display device.
A field emission type cold cathode element according to a first aspect of the present invention comprises: a substrate; a plurality of semiconductor layers formed on said substrate; an insulating film formed on said semiconductor layers; a gate electrode formed on said insulating film; a plurality of emitter holes formed in said gate electrode; emitters formed in said emitter holes; and an emitter electrode connected with said emitters through said semiconductor layers. Said emitters are grouped into a plurality of emitter groups each having at least one emitter. Said emitter or emitters of each of the emitter groups are connected to each of said semiconductor layers. Besides, a common electrode is formed over said semiconductor layers via said insulating film. Said substrate consists of, e.g., a glass substrate.
In the present invention, it is preferable that said common electrode is electrically insulated from said gate electrode and emitter electrode.
Moreover, in the present invention, said gate electrode and said common electrode are preferably formed on the same insulating film.
Furthermore, in the present invention, said semiconductor layers may be formed of poly-crystalline silicon or amorphous silicon. Said insulating film may be formed of: one selected from the group consisting a silicon oxide film, a silicon nitride film, a laminated film having two or more layers of the silicon oxide film and the silicon nitride film and a film of SiOxN1xe2x88x92x (0xe2x89xa6xxe2x89xa61).
A method of fabricating a field emission type cold cathode element according to a second aspect of the present invention comprises the steps of: forming an emitter electrode on a substrate; forming a semiconductor layer so as to cover said emitter electrode and said substrate; forming an insulating film on said semiconductor layer; forming a metal film on said insulating film before patterning the same to form a gate electrode, an emitter hole, and a common electrode; removing said insulating film exclusive of the forming areas of said gate electrode and said common electrode; and forming an emitter in said emitter hole.
A method of fabricating a field emission type cold cathode element according to a third aspect of the present invention comprises the steps of: forming an emitter electrode on a substrate; forming a semiconductor layer so as to cover said emitter electrode and said substrate; forming an insulating film on said semiconductor layer; forming a metal film on said insulating film before patterning the same to form a gate electrode, an emitter hole, and a common electrode; removing said insulating film from the forming area of said emitter hole; and forming an emitter in said emitter hole.
A display device according to a fourth aspect of the present invention comprises a field emission type cold cathode element according to the first aspect of the present invention.
According to the present invention, emitters are grouped into a plurality of emitter groups each having at least one emitter, semiconductor layers are provided by emitter group, and a common electrode is formed over the semiconductor layers via an insulating film. As a result, when an emitter or emitters increase in electric potential due to a discharge or the like, the electrode functions to suppress electric current via the insulating film. This can suppress abrupt flow of electric current resulting from a discharge or the like.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.